Javascript calculating total in gridview

[parshupooja]

Hi
I am using asp.net C# and javascript.
I have a gridview with 5 columns and 14 row
column1--column2--column3--column4--column5

Column1 to column4 is textboxes wheresa column5 is label
I am trying to calculate column 5 which is (column2-column1)+(colum n4-column3)
Here is javascript i am using. When i use this it just calculates for first row of gridview.
[code=javascript]
<script language =javascript type="text/javascript">
function Total()
{
var int1=parseInt(d ocument.getElem entById("ctl00_ contentPlaceHol der_GridView1_c tl02_TextBox1") .value);

var int2 = parseInt(docume nt.getElementBy Id("ctl00_conte ntPlaceHolder_G ridView1_ctl02_ TextBox2").valu e);

var int3 = parseInt(docume nt.getElementBy Id("ctl00_conte ntPlaceHolder_G ridView1_ctl02_ TextBox3").valu e);

var int4 = parseInt(docume nt.getElementBy Id("ctl00_conte ntPlaceHolder_G ridView1_ctl02_ TextBox4").valu e);

var int5 = (int2-int1+int4-int3);
document.getEle mentById("ctl00 _contentPlaceHo lder_GridView1_ ctl02_lblTotalH r").innerTex t = int5;

}

</script>

[/code]

i have tried using document.getEle mentById("<%=Te xtBox1.ClientID %>") and

document.getEle mentById("<%=Gr idView1.TextBox 1.ClientID%>") but throws error

plz help